The present invention relates to a method and a device for determining at least a date of a coordinated universal time, a so-called UTC date, with the aid of satellite-based positioning and date-stamping systems.
The present invention can be implemented more particularly, although not exclusively, on an aircraft, in particular a transport airplane.
The present invention applies to the field of radio navigation and to the management of time for satellite-based positioning and date-stamping systems, of GNSS (“Global Navigation Satellite System”) type.
It is known that a GNSS system uses constellations of navigation satellites and can correspond, in particular, to one of the following systems:                the GPS system (“Global Positioning System”);        the Galileo system;        the Beidou system, etc.        
Such a GNSS system, when it is embedded onboard an aircraft, provides the aircraft with, in particular, a time source, in addition to other information, such as position information.
In a customary manner, the time calculated in a GNSS system using the GPS system is based on a GPS time. The GPS time transmitted by satellites of the GPS system is composed of two values:                a value in seconds: GPS TOW (for “Time Of the Week”): 0 to 604800 s; and        a value in weeks: GPS WN (“Week Number”): 0 to 1023 weeks.        
Because of these characteristics, there exists an ambiguity of 1023 weeks per date for the GPS system. For example, knowing that the initial reference time of the GPS system starts in the night of 5 Jan. 1980 to 6 Jan. 1980 at midnight, a GPS TOW value equal to zero seconds and a GPS WN value equal to zero weeks correspond, in particular, to the following various UTC (for “Universal Time Coordinated,” i.e., “coordinated universal time”) dates:                the night of Jan. 5, 1980 to Jan. 6, 1980 at midnight;        the night of Aug. 14, 1999 to Aug. 15, 1999 at midnight;        the night of Mar. 23, 2019 to Mar. 24, 2019 at midnight, etc.        
An initialization of the UTC time data is therefore necessary in order to identify the correct UTC date from among the various possible dates.